Optimum modulator bias systems and methods in coherent optical transmitters

Abstract

A modulator bias selection method, a coherent optical transmitter, and optical modulator solve the problem of generating a correct constellation using the bias points with the minimum phase adjustment range. The optimum modulator bias systems and methods include a coherent optical transmitter with control of four (XI, XQ, YI, YQ) quadrature data signals via a transmitter (Tx) application specific integrated circuit (ASIC), with a modulator bias controller which implements an algorithm to find the optimum bias points. The optimum bias points yield a correct constellation with minimum phase / bias adjustment. An algorithm is used to find the optimum bias solution using fast, simple method, adjusting only one quadrature at a time and exploiting a control feature of the Tx ASIC. This algorithm is significantly simpler than a generalized search, is a local algorithm, and uses only DC power measurement at the transmitter.

Description

FIELD OF THE DISCLOSURE[0001]The present disclosure relates generally to optical communication systems and methods. More particularly, the present disclosure relates to optimum modulator bias systems and methods in coherent optical transmitters.BACKGROUND OF THE DISCLOSURE[0002]In next generation optical modems (e.g., 100 Gb / s and beyond), and in particular in transmitters, there is a requirement for greater optical performance (via better control of optical modulators) and for allowing a wider choice of vendors / technologies (i.e. different lithium niobate (LiNbO3) modulator vendors or indium phosphide (InP) photonic integration technologies). In particular, the new InP technology is prized for its small size and anticipated lower cost (and consequently is proposed to be used in next gen small-form-factor pluggable optics). One of the most important functions of transmitter control is to bias a modulator so it transmits a distortion free and correct optical data constellation via se...

AI Technical Summary

Benefits of technology

The patent describes a method for optimizing the bias of an optical modulator by selecting the minimum bias point and the half-power bias point of each inner and outer phase adjuster. The method includes steps of sweeping the left and right phase adjusters to find the minimum bias point, and then selecting the smaller of the two phase adjusters for the setting step. The method can be performed using a local algorithm and can be used in a coherent optical transmitter. The technical effect of the method is to improve the performance and stability of the optical modulator system.

Problems solved by technology

Using lithium niobate modulators, a generalized search can be implemented to find “reasonable” bias points, but these are not necessarily optimum points.

InP technology has a relatively small phase adjustment range and thus, if a poor hardware scheme and algorithm for bias point selection is used, the correct constellation cannot be generated or unnecessary cost is added due to rejected modulators.

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